1. Field of the Invention
The present invention relates to a light-transmitting electromagnetic wave-shielding material, in particular a light-transmitting electromagnetic wave-shielding material having a light interference fringe prevention capability.
2. Description of the Related Art
In these years, there has emerged a big problem that malfunctions or communication failures are caused in machines or electronic devices and apparatuses by electromagnetic waves generated from electronic devices and apparatuses such as personal computers, cellular phones, flat panel displays typified by liquid crystal displays and plasma displays, touch panels, car navigation systems, portable information terminals and portable game machines. Additionally, there has been pointed out a possibility that electromagnetic waves adversely affect human bodies, and hence various countermeasures have been taken with various electromagnetic wave-shielding materials for the purpose of preventing so-called electromagnetic wave interference (hereinafter referred to as EMI).
As base substrates for light-transmitting electromagnetic wave-shielding materials, there are used transparent resin sheets made of resins such as polyethylene terephthalate (PET) resin, polyethylene naphthalate resin, polyester resin and polycarbonate resin. For the purpose of improving mechanical strength and heat resistance, these resins are applied with a stretching treatment in which these resins are uniaxially stretched or biaxially stretched (see Japanese Patent Laid-Open Nos. 2006-157040, 2006-319251, 10-335884 and 10-41682). In the cases where these electromagnetic wave-shielding materials are used in the displays of electronic devices and apparatuses including polarizing plates or retardation plates, there is a problem that when displays are seen through sunglasses, goggles, glare-proof panels or glare-proof window materials having polarizing capability, light interference fringes are generated under the influences of the molecular orientation and the unevenness in the molecular orientation of the base substrates to remarkably degrade the visibility.